The Chemoprevention Branch of the Division of Cancer Prevention and Control at the National Cancer Institute has developed a program to identify and develop for human use drugs which will prevent or suppress the development of cancer. "Cancer chemoprevention" refers to the prevention of invasive neoplasia with drugs. As part of this program, the Chemoprevention Branch is seeking to develop and validate intermediate endpoint biomarkers of cancer, i.e., precancerous biological and/or molecular changes in target epithelium that correlate with cancer and that can be modulated with a chemopreventive agent. Such intermediate endpoint biomarkers will significantly shorten the time required for clinical efficacy evaluation for promising chemopreventive agents. Progress in chemopreventive drug development is being seriously slowed by the lack of surrogate endpoint biomarkers (SEB) which can serve as earlier, shorter and less expensive substitutes for cancer incidence reduction on clinical trials. Phase 2 trials in chemoprevention evaluate safety and efficacy in the modulation of surrogate endpoint biomarkers of cancer.